1. Field of the Invention
This invention relates to a heat storage device for storing a heat transfer medium, such as water, for air conditioning of a building structure or the like.
2. Description of the Prior Art
As a prior art heat storage device which is said to provide an excellent constant temperature layer and have a satisfactory heat efficiency, there is an "overflow weir/underflow weir" type heat storage tank. This type of tank, as shown in FIG. 4, is partitioned by wall 1 into sub-tanks 2a and 2b. Sub-tank 2a is provided with an overflow weir 3 open to the upper part of the tank. Sub-tank 2b is provided with an underflow weir 4 open to the lower part of the tank. Weirs 3 and 4 are provided on the opposite sides of wall 1, and the two sub-tanks 2a and 2b are in communication with each other through passage 5 formed in the partition wall 1.
It has been known in the art, in order to be able to promote the constant temperature layer of this type of heat storage tank, that the velocity [v(m/sec)] of in-flow and out-flow of water of the sub-tanks 2a and 2b at the edges of the underflow and overflow weirs has to be set to meet the following condition: Field number Fr is EQU FR=v/(d.multidot.g.multidot..DELTA..rho./.rho.).sup.1/2 .ltoreq.1
where d is the distance (in m) of the upper edge of the overflow weir 3 from the water surface, which is equal to the distance of the lower edge of the underflow weir 4 from the bottom of the water tank, g is the gravitational acceleration, i.e., 9.8 (m/sec.sup.2.), .DELTA..rho. is the difference (in kg/m.sup.3) between the velocity of in-flow of water and the density of cold or hot water in the sub-tanks and .rho. is the density (in kg/m.sup.3) of cold or hot water.
In actual use of the heat storage device, however, the water level therein is always varying due to the control of the rate of flow of cold or hot water for recirculation according to the start and stop of a recirculating pump or variations of the air conditioning load. For this reason, it is likely that the above inequality fails to hold due to reduction of the value of d and/or increase of the velocity v, thus promoting the thermal diffusion due to mixing of water to reduce the energy of the cold or hot water so as to reduce the heat storage efficiency.
In addition, the overflow weir/underflow weir type heat storage tank is required to reduce the volume of the inner space of the overflow weir 3 and underflow weir 4 in order to reduce the zone where mixing of water and thermal diffusion take place. Further, the partition wall 1 is sometimes inevitably large, as in the case of FIG. 4, due to such cause as an underground beam footing. Furthermore, it is extremely difficult to make repairs in a zone surrounded by the overflow weir 3 and underflow weir 4, particularly a repair of water-proof layers.